The present invention relates in general to methods and sprinkler apparatus for irrigating agricultural fields. More specifically, the present invention relates to traveling sprinklers used to water large fields under agricultural cultivation wherein the sprinkler must traverse fairly large land areas in a continuous and fully automatic manner so as to apply needed water with a minimum of attention from an operator.
A common approach to the problem of irrigating a large area heretofore has been to utilize a self-propelled irrigation system which pivots around a central source of irrigation water and irrigates a generally circular configured area. These center-pivot irrigation systems generally consist of a plurality of individual units aligned in a linear series, each individual unit being provided with propulsion means for rotating about a center pivot. An alignment control device is required to keep the individual units in a linear alignment extending radially outward from the center pivot. These center pivot systems are generally limited to use in very large agricultural fields, which are typically square and at least one-half mile on a side. As water is distributed over a generally circular area, the corners of the agricultural field are often inadequately irrigated.
In addition to the terrain limitations inherent in a center-pivot system, such systems typically require an input water flow volume of at least 500 gallons per minute in order to adequately pressurize a distribution system, which is typically at least one-quarter mile long and which continuously applies water to the field being irrigated. With large quantities of water continually dispensed from the system, water is generally discharged onto the field as fast as it is received in order to avoid unnecessary accumulations which might weigh the system down. In U.S. Pat. No. 3,610,531 to Erickson, for example, linear traveling sprinkler apparatus is shown in which the sprinklers are operated while the system is stopped, energy from the flowing water is stored in a spring, and the stored energy is used to move the sprinkler line only when it is substantially empty.
Also, most center pivot systems are limited in application to use in areas where the nature of the soil permits a high rate of penetration of the irrigation water beneath the surface. This is necessitated by the continuous application of large volumes of water by the system. Additionally, the soil must have high load bearing properties when it is wet in order to support the drive wheels of the irrigation units and provide traction therefor.
Other types of traveling sprinklers have been known heretofore, such as in prior U.S. Pat. No. 1,142,448, which traverse a strip configured portion of a field. This type of sprinkler travels along a cable, sprinkling continuously across the field as it is propelled by means of a cable wind-up reel. They are not designed for large area coverage such as a farm field or golf course, and are generally incapable of providing a relatively low irrigation rate to the area they do cover.
Another approach to solving the problem of irrigating a large area involves the use of an in-ground system in which sprinkler heads are distributed over the field and supplied with water by an underground conduit network. While such systems have been provided with intermittent type sprinklers to reduce the rate at which water is applied, the initial capital and installation costs are high and, unless relatively large amounts of water are required on a fairly regular basis, may be prohibitive.
Certain irrigation applications require a more flexible solution than available heretofore; one which is easily adaptable to smaller, irregularly shaped fields and is less expensive and less complex than the systems used in the large fields. More importantly, there exists a need for a relatively low cost, auxiliary or supplemental type irrigation system for use in localities which generally have adequate rain fall, but which are subject to unusually dry periods when temporary irrigation is required. In such localities the high costs of heretofore available large areas systems may have inhibited the installation of any system at all.
In addition, there are irrigation needs where the type of soil under irrigation will not accept the amount of water which may otherwise be required to operate the sprinkler system. There is accordingly a need for a sprinkler irrigation system adaptable for use in areas where the soil does not allow rapid penetration of water, or is structurally unable to support and provide traction for the drive wheels of the system.